In recent years, standard mounting of an optical disk apparatus on a personal computer has been rapidly progressed, and accordingly the optical disk apparatus as well as a hard disk drive have become indispensable to the personal computer. Initially the CD-ROM drive has constituted the majority of the optical disk apparatus, while nowadays a DVD-ROM drive having a larger capacity than the CD-ROM drive, or a writable or rewritable CD-R/CD-RW drive is normally mounted on the personal computer, and further a DVD-R or DVD-RAM drive comes on a market. As described above, the efficiency and function of the optical disk apparatus has been enhanced continuingly.
FIG. 10 is a schematic diagram illustrating a whole conventional optical disk apparatus. In the figure, numeral 11 denotes a disk, numeral 12 denotes a spindle motor, numeral 13 denotes a pickup, numeral 14 denotes a lens, numeral 15 denotes a feed, numeral 16 denotes a feed motor, numeral 17 denotes a driver IC, numeral 18 denotes an analog front end IC, numeral 19 denotes a digital signal processor IC, numeral 20 denotes a decoder, numeral 21 denotes a CPU, and numeral 22 denotes a host.
FIG. 11 is an explanation drawing illustrating a constitution of a pickup of an optical disk apparatus. In the figure, numeral 13 denotes a pickup, numeral 14 denotes a lens, and numerals 25 and 26 denote wires for supporting the lens 14 in a housing of the pickup 13.
Next, a data reading operation of the optical disk apparatus will be described.
The disk 11 is controlled by the spindle motor 12 for rotating at a constant linear velocity or a constant angular velocity. The pickup 13, moving from the inner track side to the outer track side in the radial direction of the disk 11, applies a laser beam to the surface of the disk 11 and receives light reflected therefrom, thereby reading data on the disk 11. Data called pit are spirally recorded on the disk 11, and the number of the spirals in the radial direction is referred to as the number of tracks. To accurately read the data on the disk 11, the pickup 13 drives the lens 14 in a direction perpendicular to the disk surface, thereby focusing the laser beam onto the disk 11. Further, the pickup 13 receives the reflected light from the disk 11 and detects a deviation from the center of a track. A tracking control for moving the lens 14 horizontally in the radial direction of the disk 11 is performed so that the deviation is eliminated and the laser beam is applied to the center of the track. When the lens 14 is a prescribed distance or more apart from the center of the housing, the feed 15 to which the pickup 13 is fixed is moved to return the lens 14 to the center of the housing. A focus and tracking control of the lens 14 is performed by the driver 17 according to a command of the CPU 21, and the data which are accurately read are transferred to the host 22 via the analog front end IC 18, the digital signal processor IC 19 and the decoder IC 20.
Next, influence which are exerted by the deviation of the lens in the pickup upon the data reading operation will be described with reference to FIG. 12.
FIG. 12 is a diagram for explaining the influences exerted by the deviation of the lens in the pickup upon the data reading. In the figure, numeral 11 denotes the disk, numerals 32 and 33 denote lenses, numeral 34 denotes a laser, and numeral 35 denotes a photo acceptance element.
The lens 32, which is located at the center in the pickup, refracts light from the laser 34, thereby obtaining a focus on the disk 11. Then, the disk 11 returns a reflected light to the photo acceptance element 35. However, the lens 33, which is in a position deviated from the center in the pickup, may cause the reflected light from the disk 11 to be out of the photo acceptance unit 35, as shown by a dotted line in FIG. 12. In this case, a tracking servo cannot generate a signal for detecting a position on the basis of the reflected light from the disk 11. Therefore, the optical disk apparatus cannot read data accurately due to the deviation of the lens, resulting in unstable tracking.
Next, a seek operation for accurately performing the data reading operation will be described.
The optical disk apparatus performs the seek operation to read data accurately.
In this operation, when the pickup 13 is moved to an arbitrary position on the disk 11 in accordance with a command from the outside such as the host 22, the number of tracks from the current read position to a target position is obtained by calculation, and the pickup 13 or the lens 14 is moved by the obtained number of tracks, thereby adjusting the reading position. This seek operation has two kinds of operation, i.e., feed seek and kick seek. The feed seek is one which moves the feed 15 to move the pickup 13 to a target position, which is employed for a relatively long-distance movement. The kick seek is one which moves the lens 14 after the feed seek in the housing of the pickup 13 to reach a track in a target position, which is employed for a relatively short-distance movement.
Here, the feed seek will be described with reference to FIGS. 11 and 13.
FIGS. 13(a) and 13(b) are diagrams for explaining positional changes of the lens at the feed seek, FIG. 13(a) illustrating a case where the feed is moved in an inner radial direction and FIG. 13(b) illustrating a case where the feed is moved in an outer radial direction. In the figure, numeral 13 denotes a pickup, numeral 14 denotes a lens, and numeral 15 denotes a feed.
The conventional optical disk apparatus is quite vulnerable to external vibrations or the like, because the lens 14 is supported by wires 25 and 26 in the pickup 13 as shown in FIG. 11. However, since the feed seek may be likened a kind of external vibrations, the lens 14 may be adversely deviated from the center of the pickup. 13 as shown in FIG. 13 when the feed seek is excessively accelerated or decelerated.
Next, the kick seek will be described with reference to FIGS. 14 and 15.
FIGS. 14(a) and 14(b) are diagrams for explaining positional changes of the lens at the kick seek, FIG. 14(a) illustrating a state before the kick seek and FIG. 14(b) illustrating a state after the kick seek. In the figure, numeral 13 denotes a pickup and numeral 14 denotes a lens.
In the conventional optical disk apparatus, when the lens 14 performs the kick seek from the central position in the pickup 13, the lens 14 is deviated in the pickup 13 by the kick seek as shown by a dotted line in FIG. 14(a) unless the feed 15 is subsidiarily moved. However, since the driver 17 drives the feed motor 16, thereby subsidiarily moving the feed 15 by a reference feed shifting amount F0, the lens 14 is located at the center in the pickup 13 after the kick seek. This reference feed shifting amount F0 is calculated by the CPU 21, and its calculating means will be described hereinafter.
FIG. 15 is a block diagram illustrating a means for calculating the feed shifting amount in the CPU of the conventional optical disk apparatus. In the figure, numeral 3 denotes a number-of-kick-seek-tracks calculating means for calculating the number of tracks by which the lens is moved at the kick seek, and numeral 5 denotes a reference feed shifting amount calculating means for calculating the quantity by which the feed is subsidiarily moved at the kick seek.
In the figure, the number-of-kick-seek-tracks calculating means 3 calculates the number of kick seek tracks on the basis data of the current position and a target position of the lens 14, just before the kick seek starts, which corresponds to a moving distance of the lens 14 at the kick seek. The reference feed shifting amount calculating means 5 calculates the reference feed shifting amount on the basis of the number of kick seek tracks, and outputs the calculated amount to the driver 17.
Problems of the conventional optical disk apparatus will be described with reference to FIGS. 16 and 17.
FIGS. 16(a) and 16(b) are diagrams for explaining problems at the kick seek from a state where the lens is deviated, FIG. 16(a) illustrating a state before the kick seek and FIG. 16(b) illustrating a state after the kick seek. In the figure, numeral 13 denotes a pickup and numeral 14 denotes a lens.
In the conventional optical disk apparatus, when the kick seek is performed from a state where the lens 14 is deviated in the pickup 13, the lens 14 is located at the center in the pickup 13 as shown by a dotted line in FIG. 16(a). Further, when the feed is subsidiarily moved by the reference feed shifting amount F0, the lens 14 is returned to the deviated state before the kick seek again, as shown in FIG. 16(b). As described above, in the conventional optical disk apparatus, even when the kick seek is performed from a state where the lens 14 is deviated in the pickup 13 and the feed is subsidiarily moved by the reference feed shifting amount F0, the deviated state of the lens 14 as before the kick seek is merely retained and the deviation of the lens 14 is not at all eliminated also after the kick seek as shown in FIG. 16(b).
FIGS. 17(a) and 17(b) are diagrams for explaining problems at kick seek from a state where the feed keeps moving by the inertia of feed seek, FIG. 17(a) illustrating a state after the feed seek and FIG. 17(b) illustrating a state after the kick seek. In the figure, numeral 13 denotes a pickup and numeral 14 denotes a lens.
In the conventional optical disk apparatus, even when the lens 14 is located at the central position of the pickup 13 after the feed seek, when the kick seek is performed from a state where the feed keeps moving by the inertia of the feed seek before the kick seek and the feed is subsidiarily moved for the reference feed shifting amount, the lens 14 is deviated in the pickup 13 as shown in FIG. 17(b). When acceleration or deceleration of the feed seek is excessive, the inertia of the feed seek is increased, whereby this is easier to occur.
The present invention is made to solve the above-mentioned problems and has for its object to provide an optical disk apparatus in which a lens is located at the center in a housing of a pickup after the kick seek, thereby enabling to perform subsequent tracking stably.